Liquid dispensing devices have been on the market for ages. Many of them rely on a pressurized gas raising the pressure in the interior of a container containing the liquid to be dispensed, in particular a beverage like beer or other carbonated beverages. The gas is either fed directly into the container containing the liquid like e.g., in U.S. Pat. No. 5,199,609 or between an external, rather stiff container and an inner, flexible vessel (e.g., a bag or a flexible bottle) containing the liquid to be dispensed, like in U.S. Pat. No. 5,240,144 (cf. FIGS. 1(a)&(b)). Both applications have their pros and cons which are well known to the persons skilled in the art. The present invention applies equally to both types of delivery systems.
The over pressure applied to the container for driving the liquid out thereof is usually of the order of 0.5 to 1.0 bar (above atmospheric). It is clear that the flow of a liquid reaching the dispensing tap at such high pressure could easily become uncontrollable and such sudden pressure drop could lead to sputter and to the formation of unwanted foam. For this reason, it is often necessary to provide means for substantially reducing the pressure of a liquid being dispensed between the container it is extracted from and the tap, where it contacts atmospheric conditions. Several solutions have been proposed to solve this problem.
The simplest method for inducing pressure losses between the container and the dispensing tap is to provide a long dispensing line, of a length of about 1 to 5 m. This solution is self evident in most pubs, wherein the kegs are stored in a cellar or next room, connected to the tap by a long line. For smaller systems like home dispensers, however, this solution has drawbacks, such as requiring a specific handling for fitting such long line in a dispensing apparatus, usually coiling it. A substantial amount of liquid remains in the line after each dispensing. Said stagnant liquid is the first to flow out of the tap at the next dispense. This of course has the inconvenience that the beverage stored in the dispensing line is not controlled thermally and would result in dispensing e.g., beer at a temperature above the desired serving temperature. A further inconvenient is when changing container, the liquid stored in the line may yield serious hygienic concerns and, in case of a different beverage being mounted on the appliance, to undesired flavours mixing. For solving this latter problem, it has been proposed to change the dispensing line each time the container is being changed (cf. e.g., WO2007/019853, dispensing line 32 in FIGS. 35, 37, and 38).
An alternative to increasing the length of the dispensing line for generating pressure losses in a flowing liquid is to vary the cross-sectional area of the line. For instance, it is proposed in WO2007/019852 to provide dispensing lines comprising at least two sections, a first, upstream section having a cross-sectional area smaller than a second, downstream section. Such line can be manufactured by joining two tubes of different diameter, or by deformation of a polymeric tube, preferably by cold rolling. US2009/0108031 discloses a dispensing line comprising at least three sections of different cross-sectional area forming a venturi tube as illustrated in FIGS. 5 and 9 of said application. The dispensing tube described therein is manufactured by injection moulding two half shells each comprising an open channel with matching geometry to form upon joining thereof a closed channel with the desired venturi geometry. In DE102007001215 a linear tube section at the inlet of a pressure reducing duct transitions smoothly into a tubular spiral with progressively increasing diameter, finishing in an outlet opening.
U.S. Pat. No. 5,573,145 proposes to reduce pressure of an outflowing liquid by inserting in the dispensing line, upstream from the tap, a device for reducing foaming and flowrate of the liquid. Said flow regulating device consists of a mesh rolled up to form a cylinder and acts as a static mixer. A static mixer is actually the solution taught in AU2008/240331 to reduce the pressure of a liquid flowing out of a dispensing apparatus.
An effective but rather expensive and hygienically sensitive solution to reducing the pressure of the flowing liquid is to interpose in the dispensing line a pressure controlling valve between the container and the tap.
The solutions to reducing the pressure of a flowing liquid reviewed supra are all relatively expensive as they all require some degree of assembly. The cost of a dispensing line relative to the volume of beverage dispensed therewith may appear insignificant if it can be used several times, or is to be mounted on a fixed dispensing apparatus. Recently, a market for stand-alone home appliances has been developing rapidly. In particular, some of these appliances are not meant to be reloaded after use with a new container and should be disposed of once the original container is empty. It is clear that the design of such all-in-one, ready-to-use, disposable appliances is severely cost driven, as the cost of the packaging and dispensing mechanism should not unreasonably outweigh the cost of the beverage to be dispensed, and sold in relatively small quantities in a container of a capacity of the order of 1 to 10 l, maybe up to 20 l. Furthermore, recycling of the components of disposable appliances is a problem which cannot be overlooked nowadays. In such small appliances, the pressure reducing tube may have quite a small diameter and preferably comprise a curved shape in order to create pressure losses as the liquid flows through the tube.
Pressure reducing units comprising a curvilinear channel of small and possible varying cross-section can be produced e.g., by injection moulding a first half shell comprising a first open half channel and a second half shell comprising a second half of channel, matching the first one, and welding the two half shells, with the two half channels in registry, by injection moulding an adhesive at the interface. The adhesive can be the same material of the two half shells, or it may be a different one, such as an elastomer or crosslinking adhesive. Such process is disclosed e.g., in JP7217755, EP1088640, DE10211663, and JP4331879. The channel walls should be smooth and impervious to the liquid to be dispensed. The problem with the foregoing production technique is that it is very difficult to bring just enough welding material to fill the joint between the two half shells to be flush with the channel walls. As illustrated in FIG. 2(a), if there is not enough welding material, a recess (4r) is formed which may substantially change the flow behaviour of the liquid. On the other hand, as illustrated in FIG. 2(b), if too much welding material is injected, it may form a flash (4f) protruding into the channel, locally reducing its cross-section and, in extreme cases, even sealing the passage altogether, in particular for channels of small cross sections.
It therefore remains a need for providing pressure regulating and flow limiting lines in a pressure driven liquid dispensing apparatus which is effective in controlling the pressure and flow rate of a liquid, which can be produced economically and reproducibly.